// Source : https://leetcode.com/problems/convert-a-number-to-hexadecimal/
// Author : Hao Chen
// Date   : 2016-11-12

/*************************************************************************************** 
 *
 * Given an integer, write an algorithm to convert it to hexadecimal. For negative 
 * integer, two’s complement method is used.
 * 
 * Note:
 * 
 * All letters in hexadecimal (a-f) must be in lowercase.
 * The hexadecimal string must not contain extra leading 0s. If the number is zero, it 
 * is represented by a single zero character '0'; otherwise, the first character in the 
 * hexadecimal string will not be the zero character.
 * The given number is guaranteed to fit within the range of a 32-bit signed integer.
 * You must not use any method provided by the library which converts/formats the 
 * number to hex directly.
 * 
 * Example 1:
 * 
 * Input:
 * 26
 * 
 * Output:
 * "1a"
 * 
 * Example 2:
 * 
 * Input:
 * -1
 * 
 * Output:
 * "ffffffff"
 ***************************************************************************************/

class Solution {
public:

    string toHex(int num) {
        
        if (num == 0) return "0";
        
        unsigned int x = num;

        string result;
        for(;x > 0; x/=16) {
            int n = x % 16;
            char c;
            if (n < 10) c = n + '0';
            else c = 'a' + n - 10 ;
            result = c + result;
        }
        return result;
    }
};